- If a text format property defines the 'optional' attribute as true,
then the $required parameter that
is passed to \core\external\exporter::get_format_structure() should be
VALUE_OPTIONAL.
- If a default value is provided for a format property,
\core\external\exporter::get_format_structure() should pass the default
value to the external_format_value constructor.
- Added validation for external_format_value for the default parameter.
Debugging will be shown in case an invalid default value is passed.
- Amended unit tests for better coverage.
Jun Pataleta